Lifestyle modification is urgently recommended to combat obesity and diabetes, yet very little is known about the implementation of large-scale lifestyle change programs in real-world clinical settings. The VA's MOVE program is the largest lifestyle change program nationwide, with over 400,000 participants since 2005. We will address three Aims: (1) To determine the extent to which disparities affect enrollment and participation in MOVE; (2) To determine the extent to which participation in MOVE improves cardio-metabolic risk; and (3) To determine the impact of participation on healthcare system resource use and costs. National data are available from the VA's Corporate Data Warehouse, and analyses will be conducted using SAS within the VA Informatics and Computing Infrastructure (VINCI), a high-performance secure computing environment. Veterans who meet eligibility criteria for MOVE participation, with at least 3 consecutive years of VA primary care from 2005 to 2012, will be included. Multiple modeling strategies, including generalized estimating equations, will be used to appropriately analyze longitudinal data. This research has the potential to profoundly impact the field of diabetes prevention. Expected results include groundbreaking knowledge of a national, clinically-based program's reach and impact on patient health and the health system. The work is unique in several key areas: (1) MOVE is the largest weight loss program nationwide; (2) MOVE is implemented within a clinical setting, unlike more common community-based approaches; (3) MOVE is a real-world program in which participants are patients recommended for weight loss by their primary care providers, rather than study volunteers; (4) the proposed research examines MOVE's impacts on both individual-level health outcomes and health system-level costs and resource use. While outcomes are expected to be more modest in MOVE than in the Diabetes Prevention Program (DPP), preliminary data indicate that MOVE participation substantially reduces diabetes incidence. The proposed work will examine improvements in BMI, CVD risk factors, diabetes and CVD incidence, medication usage, and health system costs and resource use. This research will also inform future work, such as an expected-benefits algorithm and EHR tool to provide healthcare professionals and patients with individualized recommendations. Nearly three quarters of veterans in the VA health system are overweight or obese; thus, approximately 6 million veterans stand to benefit from MOVE if it is found to be effective. In addition to evaluating the program's health and health system impacts, the proposed research will inform improvements in MOVE implementation by identifying disparities in program participation as well as provider- and facility-level factors associated wit reduced disparities. This work is also relevant outside of the VA, as lessons learned from these analyses will inform other health care systems where many more millions of Americans could benefit from lifestyle change programs similar to MOVE.